This invention relates generally to the facet passivation of semiconductor light emitting devices by the reactive reduction of contaminants thereon and more particularly to a passivating layer deposited on the cleaved facet of semiconductor lasers, LED's or the like and the method of deposition thereof.
Facet damage due to mirror oxidation when, for example, a cleaved facet of a semiconductor laser is exposed to the atmosphere is a major mechanism of gradual and catastropic mirror degradation. See, for example, the Article of T. Yuasia et al, "Degradation of (AlGa)As DH Lasers Due to Facet Oxidation," Applied physics Letters, 32(2), pp. 119-121 (Jan. 15, 1978); C. H. Henry et al, "Catastrophic Damage of AlGaAs Double-Heterostructure Laser Material", Journal of Applied Physics, 50, p. 3721 (1979); F. R. Nash et al, "Facet Oxide Formation and Degradation of GaAs Lasers", Journal of Applied Physics, 59(5) pp. 3133-3441; F. R. Nash et al, "GaAs Laser Reliability and Protective Facet Coatings", Journal of Applied Physics, 50(5) pp. 3122-3132 (May, 1979); and John A. F. Peek, "Water Vapor, Facet Erosion, and the Degradation of (Al,Ga)As DH Lasers Operated at CW Output Powers of Up to 3 mW/.mu. Stripewidth", IEEE Journal of Quantum Electronics, Vol. QE-17, No. 5, pp. 781-786 (May 1981). Also, see U.S. Pat. Nos. 4,178,564 and 4,337,443. From these references, it has been known that atmospheric exposure of laser facets form a passivation film or coating of transparent insulative materials, such as SiO.sub.2, Al.sub.2 O.sub.3, MgO, ZnO, TiO.sub.2, Si.sub.3 N.sub.4, etc., on the exposed facets of a semiconductor laser. The purpose of the facet coating is to protect the laser from the ambient atmosphere, oxidation and resulting facet erosion upon operational use of the laser. The coating reduces threshold current, increases external differential quantum efficiency, and increases the catastrophic degradation. Without some type of protection, catastrophic degradation may occur after a period of use, requiring laser replacement.
While the coating on the laser facet protects it from the ambient, facet degradation still occurs due to the presence of at least some contaminants on the facet on the original surface at the interface with the protective overcoating in spite of careful cleaning of the facet surface prior to passivation coating.
Recently, it has been suggested that facet erosion may be suppressed by employing ion milling techniques on the facet surface prior to mirror coating. See the Article of Mizuishi et al, "The Effect of Sputtered - SiO.sub.2 Facet Coating Films on the Suppression of Self-Sustained Pulsations in the Output of (GaAl)As Double Heterostructure Lasers During CW Operation", IEEE Journal of Quantum Electronics, QE-16(7), pp. 728-734 (July, 1980). This technique involves ion milling the laser facet surface to a predetermined depth to remove facet contamination followed by the deposition of a protective coating to increase the laser lifetime.
However, it has been observed that ion beam damage resulting to the laser facet can be significant, particularly if the depth of surface damage is sufficiently large as a few hundred angstroms. See, for example, the discussion in the Articles of S. K. Ghandhi et al, "Ion Beam Damage Effects During the Low Energy Cleaning of GaAs", IEEE Electron Device Letters, Vol. EDL-3(2), pp, 48-50 (February 1982) and M. Kawabe et al, "Effects of Ion Etching on the Properties of GaAs", Applied Optics, Vol. 7(16), pp. 2556-2561 (Aug. 15, 1978).
The primary objective of this invention is to overcome the above-mentioned difficulties in providing more durable passivation coatings on semiconductor light emitting devices, such as lasers, LEDs or the like, without the requirement of ion milling techniques. It covers such devices both with and without subsquent overcoating, both reflective and antireflective.